Pretreatment of Wood for Measuring Tree-Ring Nitrogen Paul R. Sheppard Lab. of Tree-Ring Research and Mary A. Topa Boyce Thompson Inst. Plant Research

Dendrochemistry of Nitrogen Can ring-N elucidate N availability of the past? N mobility (sap chemistry) –Poulson et al. (1995): “N concentration variation in tree rings cannot provide information on past environmental availability of N …”

What If Wood Is “Cleaned”? Heartwood extractives: No N, but mass Sapwood: Sap has organic N compounds Cell walls have N –Does this component reflect N availability at time of ring formation?

Wood Treatments Chemical Treatments –Organic solvents –Oxidizers –Reducers Physical Treatments –Autoclaving –Microwaving –Pulverizing

Loblolly pine of North Carolina 6-year-old trees in 2001 All trees N fertilized every year Some trees 15 N enriched in their 5 th year (1999) Other trees left at natural abundance Pre-enriched δ 15 N = natural abundance? Study Details

Conclusions (so far) Measuring ring N right out of tree could be problematic –either δN or N content Combination of physical-chemical wood pretreatments works well –eliminate sap/cytoplasmic N compounds

Can We Do Better? Pre-enriched δN (+18) not quite natural abundance Some other physical/chemical treatment? Parenchyma effect? –Fiber separation? –Ring N content of 0.01%, too low

Hangarter (web notes): –“extensin produced is dependent on mechanical wounding, infection” Cowling and Merrill (1966): –“N content of cambial zone varies with … nutritional status …” –Extend to tracheids of tree rings? N Content of Cells